questions about vibracaster

[cnspedalbuilder]

Anyone out there build the Rick Holt Vibracaster? I have been meaning to build a dual pedal with a  Rangemaster going in to the Vibracaster. Schematic for the vibracaster alone is here:
http://s9.postimage.org/aapufpncf/Vibracaster_V3.jpg

Right now I have a few questions:
1. Does the Vibracaster sound like a Valvemaster boost/OD when the depth is set to zero? I previously built and loved the Valvemaster, and the idea of getting tremolo for free would be great. But if the vibracaster can't do an OD sound, that would be a different story.

2. I know the Vibracaster is designed to run at 12 Volts. Because I'm gonna box it w/a Rangemaster I was going to use a MAX1044 charge pump. So, I'd like to use the voltage doubled output of the charge pump as the input voltage to the Vibracaster. Will the Vibracaster run at 18 volts w/normal 1/4 watt components or do you need to go up to .5 or 1 watt resistors? Would you need to do any adjustments to run at 18 volts?

3. OK kind of a separate point, but has anyone noticed that the Layouts gallery on the DIYSB page seems to be DOA?

[PRR]

The tube plates will be fine at 18V.

The 12V heater MUST get 10V-14V, at too much current for a '1044. Yes, some folks run 12V heaters at 9V, but for distortion, not a semi-clean Vibrato. I suggest a 12V supply, dropped to 9V for your other stuff. Yes, that's "special", but not expensive.

> has anyone noticed that the Layouts gallery on the DIYSB page seems to be DOA?

https://www.diystompboxes.com/smfforum/index.php?topic=122389.0

[rankot]

He can also run filaments in parallel, 6.3V/300mA, using drop resistor in series with them, so he can use 9V PS.

[cnspedalbuilder]

@PRR if the heater requires too much current for a MAX1044 do you think it's not going to work to box it with the charge pumped Rangemaster? I need that to get a negative ground power supply, and I was hoping the MAX (or 7660) could do double duty.

@rankot: this would be great, but can you please clarify? I'm a tube-amateur (well amateur everything, but more so w/tubes)--I'm seeing the heater as pin 5 of the 12AU7. How would I run it in parallel and use the series resistor? Sorry if this is a dumb question.

Also, has anyone built the vibracaster and used it as an overdrive as well as tremolo?

[Marcos - Munky]

You can use a MAX1044 to power the tube plates, but not the heaters. The MAX1044 can't handle the current the heaters need.

The heaters pins are 4, 5 and 9. Look at the first 2 paragraphs of this page: http://www.valvewizard.co.uk/heater.html. Basically, you have a heater from pin 4 to pin 9, and another heater from pin 5 to pin 9. Each 12AU7 heater needs 6.3V 150mA to work. If you power them using pins 4 and 5 (pin 9 disconnected), they'll be in series and have to be powered by 12.6V 150mA (twice the voltage, same current). If you power them using pins 4+5 together and pin 9, they'll be in parallel and have to be powered by 6.3V 300mA (same voltage, twice the current).

Since the MAX1044 can't handle 12V (max in voltage is 10V), you have to run the heaters in parallel. So what you can do is power the MAX1044 from a 9V power supply, with the negative voltage powering the Rangemaster and the positive doubled voltage powering everything marked as V+ on the Vibracaster. For the heaters, forget that "pin 4 to ground and pin 5 to +12V" part. You have to use pins 4+5 and pin 9. One of them goes to ground and the other goes to a voltage drop resistor connected to the 9V supply. It doesn't matter if you'll connect 4+5 to ground and 9 to the resistor, or the other way around.

For the voltage drop resistor, you'll have to drop from 9V to 6.3V, dropping 2.7V under a current of 300mA. Using Ohm's law (V = R*i and P = V*i), you can do the maths. Basically, you'll need a 9r resistor (9r1 will do the job) that can handle 0.81W. I'd go for a 2W resistor just to be safe.

Also, for your question on "Vibracaster as a boost/od", notice the gain is fixed. So it have less gain than a Valvecaster, and you have to mod it to add a gain pot.

[Marcos - Munky]

Double post removed.

[rankot]

Since the MAX1044 can't handle 12V (max in voltage is 10V), you have to run the heaters in parallel. So what you can do is power the MAX1044 from a 9V power supply, with the negative voltage powering the Rangemaster and the positive doubled voltage powering everything marked as V+ on the Vibracaster. For the heaters, forget that "pin 4 to ground and pin 5 to +12V" part. You have to use pins 4+5 and pin 9. One of them goes to ground and the other goes to a voltage drop resistor connected to the 9V supply. It doesn't matter if you'll connect 4+5 to ground and 9 to the resistor, or the other way around.

So to clarify, connect pins 4&5 together, then connect 9.1 Ohm resistor between them and ground, and connect pin 9 to 9V. It is better to have filaments slightly elevated above cathode, thus always put that dropping resistor between ground and filaments.

[Marcos - Munky]

I usually do the other way. But as pointed by Rankot, it's better to have the heaters slightly elevated, so put the resistor between them and ground.

[frequencycentral]

Holy guacamole, that was a long time ago!

[bluebunny]

Holy guacamole, that was a long time ago!

Longevity is no bad thing, Mr Holt.   

[cnspedalbuilder]

Quote from: Marcos - Munky on Yesterday at 02:15:55 PM
Since the MAX1044 can't handle 12V (max in voltage is 10V), you have to run the heaters in parallel. So what you can do is power the MAX1044 from a 9V power supply, with the negative voltage powering the Rangemaster and the positive doubled voltage powering everything marked as V+ on the Vibracaster. For the heaters, forget that "pin 4 to ground and pin 5 to +12V" part. You have to use pins 4+5 and pin 9. One of them goes to ground and the other goes to a voltage drop resistor connected to the 9V supply. It doesn't matter if you'll connect 4+5 to ground and 9 to the resistor, or the other way around.

So to clarify, connect pins 4&5 together, then connect 9.1 Ohm resistor between them and ground, and connect pin 9 to 9V. It is better to have filaments slightly elevated above cathode, thus always put that dropping resistor between ground and filaments.

Marcos and Rankot: Let me make sure I am on board: you said that voltage doubled input (+18V) should go to V+. Do the calculations apply for +18V input or would I need to run a 39 ohm resistor between either pin 4 or 5 to ground?

For the Gain pot, where would it go? Looking at the ValveMaster schematic, https://www.diystompboxes.com/smfforum/index.php?topic=63479.3200 would you replace the 470k resistor to ground with a 500k Variable Resistor?

Frequency Central: Rick, you won't remember, but a while ago you advised me to build the ValveMaster and I loved it before I stepped on the tube and messed it up. I'm hoping to get the Vibracaster going (which you also suggested). I'm not locked into a vibracaster, just seeing if I can get double duty with a ValveMaster-like pedal that also does a tremolo (even if its a dirty onbe). If you have a newer/better design that you want to point me too, please chime in!

[Marcos - Munky]

you said that voltage doubled input (+18V) should go to V+. Do the calculations apply for +18V input or would I need to run a 39 ohm resistor between either pin 4 or 5 to ground?

+18V goes to every V+ on the schematic. Forget the pins 4 and 5 on the schematic, you'll wire them in a different way.

It's not "either pin 4 or 5", it's "both pin 4 and 5". You'll connect them together. Then you'll connect a 39ohm 2W resistor between pins 4+5 and ground, and connect pin 9 to +9V (not +18V or you'll fry your heaters). Or you can reverse this connection, doing pin 9 to the resistor and pins 4+5 to 9V, it doesn't matter. Just be sure to use a 2W resistor, and it's a nice idea to have it a little bit away from other stuff, since it'll heat up a little.

[cnspedalbuilder]

I see the issue. So to do this, would I run two separate V+ lines, one at +18 for the plates and another +9v line straight from the DC in to the heaters (bypassing the charge pump altogether)?

[Marcos - Munky]

Yeah, that's it.

[cnspedalbuilder]

I thought of another simpler solution--I have a spare +12V out from my power supply. So, maybe I could split the positive line so that one +12V goes into all of the +V inputs for the vibrocaster, and the other +12V goes to the charge pump. I think the V- output from the charge pump would be -12v, so could I run that straight into the Rangemaster? Or will I need to add a series resistor to get it down to -9V?

Thanks!

[rankot]

you said that voltage doubled input (+18V) should go to V+. Do the calculations apply for +18V input or would I need to run a 39 ohm resistor between either pin 4 or 5 to ground?

+18V goes to every V+ on the schematic. Forget the pins 4 and 5 on the schematic, you'll wire them in a different way.

It's not "either pin 4 or 5", it's "both pin 4 and 5". You'll connect them together. Then you'll connect a 39ohm 2W resistor between pins 4+5 and ground, and connect pin 9 to +9V (not +18V or you'll fry your heaters). Or you can reverse this connection, doing pin 9 to the resistor and pins 4+5 to 9V, it doesn't matter. Just be sure to use a 2W resistor, and it's a nice idea to have it a little bit away from other stuff, since it'll heat up a little.

Not 39R resistor, it shall be 9.1R or 10R! 2.7V/.3mA=9R.

[cnspedalbuilder]

OK, looking back I am thinking that the simpler option may be to run a 12V 200mA input from my DC power supply. Would that be sufficient to power everything including heaters in the Vibracaster?

Assuming that is the case, then would I run the +12V output to a resistor (3 volt drop/.2A current=15 Ohms?) to get 9V into the MAX 1044 charge pump?

Would that plan work or am I missing something? Sorry I am no engineer, so thanks for your patience! 

[willienillie]

Not 39R resistor, it shall be 9.1R or 10R! 2.7V/.3mA=9R.

.3A (300mA)

12V 200mA input from my DC power supply. Would that be sufficient to power everything including heaters in the Vibracaster?

No (see above)

[Marcos - Munky]

Not 39R resistor, it shall be 9.1R or 10R! 2.7V/.3mA=9R.

Yeah, 9r1! TC said 39r and I didn't checked the correct value. It should be 9r1 2W.

Assuming that is the case, then would I run the +12V output to a resistor (3 volt drop/.2A current=15 Ohms?) to get 9V into the MAX 1044 charge pump?

Your math is half correct and half wrong. You'll have a 3V drop, but the current going to the MAX1044 won't be 200mA. So the value of the resistor will depend on a few things, like how's the output current, which for the MAX1044 is 10mA maximum. To make it easier, you can just use an 78L09 regulator.

12V 200mA input from my DC power supply. Would that be sufficient to power everything including heaters in the Vibracaster?

No (see above)

Well... actually it may work. Using a 12V supply, it doesn't make any sense on powering the heaters with 6.3V rather than 12V. The heaters in series asks for 150mA when powering by 12V, so the power supply will handle the heaters and it'll be 50mA left for the rest of the circuit.

Why it may work and not surely work? It basically depends on two things:
1 - how much current does the rest of the circuit, the MAX1044 circuit and the Rangemaster will need? It'll probably be under 50mA.
2 - is the power supply transformer based or it's a switching one? If it's transformer based, it'll work (supposing we have an yes for the above). But if it's a switching one, it'll probably not work. The reason is the heaters have a "cold resistence" lower than the "hot resistence", so the initial current will be greater than 150mA. It's fast, but the current will have a peak for a short time. A transformer rated for 200mA can handle that current peak, but a switching circuit rated for 200mA can't and will see the low resistence/greater current as a short circuit. You can calculate how much is that current measuring the "cold resistence" of the heaters and using Ohm's law.

[willienillie]

The heaters in series asks for 150mA when powering by 12V,

You're right.  I hadn't read through all the posts thoroughly enough, and don't have the 12AU7 heater currents memorized.

But...

the heaters have a "cold resistence" lower than the "hot resistence", so the initial current will be greater than 150mA

I still wouldn't trust a 200mA 12V supply to do this job.  I don't know what the start-up (cold) heater current might be, but I think it's more than double.